This invention relates to a trigger device for a sound motion picture camera.
As is well known, a film feeding device of a sound motion picture camera includes an intermittent feeding mechanism coupled with a shutter having a claw adapted to fit in one of perforations of a film in engaging relation thereto, for feeding the film intermittently; and a continuous feeding mechanism having a capstan and pinch roller which is adapted to resiliently-contact the capstan. Both film feeding mechanisms start running at a lag therebetween, so that the capstan may start rotating prior to the actuation of the claw and the shutter. This time lag originates from the arrangement of both mechanisms. In the intermittent film-feeding mechanism, a claw and shutter drive motor is large in torque and small in load, and the running of the claw and shutter drive motor at a given speed is accomplished immediately after the starting thereof, thus enabling the claw and shutter to actuate at a given speed immediately after the starting. On the contrary, in the continuous film-feeding mechanism, a mechanism for rotating the capstan, in general, consists of a fly wheel large in inertia and a belt, and a certain time is required from the starting of the capstan motor until the rotation of the capstan at a given speed is established. Taking this lag in operation between two mechanisms into account, the capstan motor is so arranged as to start at the initial stage of the release or trigger operation.
As a result, if the timing of bringing the pinch roller into resilient-contact with the capstan is earlier than the starting of the claw and shutter, it follows that a film which is paid out of a film cartridge and loosely wound in the form of loop is shifted by the capstan and pinch roller, independently of actuation of the claw and shutter, and the following problems would result.
(a) It is usual for a sound motion picture camera that, the instant the pinch roller is brought into pressure-contact with the capstan, a film engages a record head, and the recording of sound signals thereto is started. However, since the sound-recorded film is shifted before the claw and shutter start, there is experienced in the reproduction that the sound reproduced fails to correspond to an image projected to a screen.
(b) While the claw and shutter remain imoperative, dislocation of a film takes place in the exposure aperture portion, thus leading to production of a picture having image mismatching.
(c) The film is unnecessarily pulled into tension, thus causing the idling of the capstan and pinch roller, as a result of which the pinch roller made of rubber suffers deformation due to friction relative to the film, and it becomes difficult to take the film cartridge out of the camera body, after the termination of the photographing.
On the other hand, the fact that the timing of bringing the pinch roller into resilient-contact with the capstan is earlier than the timing of starting the claw and shutter results in that, at the interruption of the trigger operation, the film continues to be fed, with the claw and shutter maintained stopped. Also in this event, the same problems as the above-described result.
To solve the above problems, a trigger device having a tumbler spring has been proposed, in which, in the process of the trigger operation, the pinch roller is brought into resilient-contact with the capstan instantaneously under the action of the tumbler spring. With this trigger device, a strong force is required for the tumbler spring, leading to the trigger operation which requires an increased operating force.